1. Field of the invention
The present invention relates to a rotory piston engine and a method for manufacturing the same. More specifically, the present invention pertains to a side housing made of an aluminum alloy having an inner surface covered with a hard ceramic material so as to improve a wear resistant property.
2. Description of the prior art
Conventionally, it is known to employ an aluminum alloy for a side housing of rotary piston engines in order to lighten the engine. It should, however, be noted that the aluminum alloy is relatively soft in hardness and, therefore, disadvantageous in the wear resistant property. Specifically, since a high wear resistant property is needed for the side housing of the rotary piston engine, it is necessary to provide means for improving a wear resistant property in the aluminum alloy side housing. For this purpose, Japanese Utility Model Publication No. 46-20083 published for opposition on July 13, 1971, discloses a side housing having an inner surface thereof covered with a flame sprayed layer of a hard metallic material whereby the side housing is brought into contact with sealing members of a rotor.
In the side housing as disclosed in the Japanese Utility Model Publication, since craters are produced through the flame spraying process to hold a lubricating oil therein to thereby provide an appropriate oil supply effect into the combustion chamber, it is desirable that the surface of the flame sprayed layer have a certain roughness in order to obtain an appropriate lubricating effect between the surface of the side housing and the sealing members of the rotor. It should, however, be noted that the surface of the flame sprayed layer is so rough as to cause undesirable wear of the sealing member. Therefore, the surface is not suitable for the inner surface of the side housing. Accordingly, it is necessary to face the portion of the surface so as to obtain an appropriate roughness thereof. It should further be noted that such hard materials are generally very expensive in comparison with other materials such as aluminum matrix of the side housing. Therefore, it is desirable to reduce the amount of the material used for the flame sprayed layer as much as possible. Under these circumstances, it has been proposed that the flame sprayed layer of a hard material is formed on only a portion of the inner surface of the side housing wherein the portion is brought into contact with the sealing members of the rotor and thereafter a certain facing treatment is applied to the portion by means of a diamond whetstone or the like in order to obtain an appropriate roughness thereof.
However, in the case where this method is applied for a side housing made of the aluminum alloy, the whetstone is inevitably brought into contact with not only the hard flame sprayed layer but also the soft aluminum alloy matrix exposed adjacent to the portion covered with the hard flame sprayed layer so that there may occur a jamming of the whetstone during the facing treatment to thereby hurt the faced surface of the side housing and affect an operation of the whetstone.